1. Field of the Invention
The present invention relates to a solid state imaging pickup device and a manufacturing method thereof, and more particularly but not limited to a solid state imaging pick device in which a charge transfer electrode is formed by processing a single-layer conductive electrode material film, characterized in that the controllability or ease of planarizing is improved when planarizing a narrow inter-electrode gap by re-flowing a film.
2. Description of the Related Art.
FIG. 1 shows a cross sectional view of a charge transfer part of a conventional solid state imaging pickup device with a singe-layer electrode structure.
The charge transfer part comprises a charge transfer part 604 that is formed by ion-implanting phosphorus in a first P-type well layer 602 and a second P-type well layer 603 formed on a N-type semiconductor substrate 601, a gate insulating film 605 formed by thermally oxidizing the surface of the N-type semiconductor substrate 601, and a charge transfer electrode 606 that is formed on the gate insulating film 605.
The charge transfer electrode 606 is formed by patterning a one-layer conductive electrode material film with an inter-electrode gap of about 0.25 xcexcm to 0.50 xcexcm.
On the charge transfer electrode 606, an inter-layer insulating film 607 is formed, and a metal shielding film 608 is provided on the inter-layer insulating film 607 to prevent the incidence of light into the charge transfer part.
Cross sectional views of the charge transfer part of a conventional solid state imaging pickup device with a single-layer electrode structure are shown in FIGS. 2 to 4 in the order of manufacturing steps.
First, a P-type well layer 702, a second P-type well layer 703, a charge transfer part 704, and a gate insulting film 705 are formed in turn on an N-type semiconductor substrate 701. Further, on the substrate 701, charge transfer electrodes 706 are formed, having an arca separating them from each other in the charge transfer direction (inter-electrode gap) of a short distance of about 0.25 xcexcm to 0.50 xcexcm (as shown in FIG. 2).
Next, an inter-layer insulating film 707 is formed on the whole surface of the device. At this moment, the inter electrode gap part has a large aspect ratio and the step-covering performance of the insulating film is poor. Therefore, a space (cavity) 709 is produced at the inter-electrode gap part, or the resulting coverage of the surface is defective and/or uneven (as shown in FIG. 3).
Next, a metal shielding film 708 or a metal wiring is formed on the interlayer insulating film 707, but there has been such a problem that a step-cut 710 is produced where the coverage on the inter-layer insulating film 707 is poor at the inter-electrode gap part, such that the shielding characteristic or the charge transfer characteristic may be degraded (as shown in FIG. 4).
A method that has been considered, in order to prevent the step-cut of the metal layer, is filling and planarizing the inter-electrode gap by using an insulator film which provides good re-flow performance when heated, after the charge transfer electrode has been patterned. The process-flow at this moment will be described by using cross sectional views in the order of steps shown in FIGS. 5 to 9.
First, a first P-type well layer 802, a second P-type well layer 803, a charge transfer part 804, and a gate insulating film 805 are formed in turn on an N-type semiconductor substrate 801. Further, on the substrate 801, charge transfer electrodes are patterned so that charge transfer electrodes 806 are formed (as shown in FIG. 5).
Next, a first inter-layer insulating film 811 is formed on the whole surface of the device, and is heat-treated, for example, in an atmosphere of nitrogen at 900xc2x0 C., thereby re-flowing, and filling up the inter-electrode gaps with the first inter-layer insulating film 811 (as shown in FIG. 6).
Next, the first inter-layer insulating film 811 is etched until the surface of the charge transfer electrodes 806 is exposed, thus forming embedded insulating films 821 (as shown in FIG. 7).
Next, a second inter-layer insulating film 812 is formed on the charge transfer electrodes 806 and the embedded insulating film 821 (as shown in FIG. 8).
Finally, a metal shielding film 808 is formed on the second inter-layer insulating film 812 (as shown in FIG. 9).
By the conventional method described above, it is possible to form the metal shielding film 808 with no step-cut.
However, the above mentioned method of re-flowing the insulating film in an attempt to fill the inter-electrode gaps has the following problems, as described below.
FIG. 10 typically shows a pattern of conventional charge transfer electrodes 906. At the part B-Bxe2x80x2, there is no adjacent electrode pattern at the terminal part of the electrode pattern, and thus, there is no xe2x80x9cwallxe2x80x9d for stopping the flow of the film during re-flowing. Therefore, there is a problem in that a fluctuation is caused in the film thickness because the film outflows during re-flowing, resulting in poor embedding performance.
FIGS. 11 and 12 show cross sectional views in the order of steps of the part B-Bxe2x80x2 in FIG. 10.
First, a first inter-layer insulating film 911 is formed after charge transfer electrodes 906 have been formed, (as shown in FIG. 11).
Next, the first inter-layer insulating film 911 is removed by etching until at least the surface of the charge transfer electrodes 906 is exposed (as shown in FIG. 12).
As this moment, the first inter-layer insulating film 911 remains at the side wall part of the terminal part of the charge transfer electrode 906, and a film thickness uneven area 913 is produced.
It is one object of the present invention to provide a highly reliable solid state imaging pickup device, in which the charge transfer electrodes are formed by patterning a singe-layer conductive electrode material film and the embedding performance is improved in the case where the inter-electrode gap parts are filled with the first inter-layer insulating film for solving the problems of the above described conventional solid state imaging pickup device.
In an embodiment of the semiconductor device of the present invention, a semiconductor device comprises a gate insulating film formed on a substrate, a plurality of charge transfer electrodes formed on the gate insulating film, and a first inter-electrode insulating film for filling a space between the plurality of charge transfer electrodes, with one charge transfer electrode surrounding at least one other charge transfer electrode.
As a result, the embedding performance of an insulating film is improved when it is re-flowed for flattening the inter-electrode gaps. This enables formation of a good metal wire or shielding film with no step-cut, and makes it possible to provide a solid state imaging pickup device with an improved reliability.